Ceria-Based Engine Exhaust Catalysts

Abstract

Ceria and ceria-based materials are a significant component of automotive three-way catalyst washcoats. Fossil fuel-powered vehicles emit pollutants such as carbon monoxide, nitrogen oxides, and unburnt hydrocarbons from fuel, and three-way catalysts are a critical technology in reducing emissions of these pollutants. Air quality issues around the world, particularly in urban areas with high vehicle density, are a major public health concern, and improving three-way catalyst performance is a significant component in addressing this concern. This thesis addresses two potential routes for improving the performance of ceria-based catalysts – doped ceria for improved low-temperature performance and graphene oxide-templated ceria to improve catalyst stability at high temperatures.

The effect of doped transition metals on ceria nanorod catalysts has been examined and tested in CO oxidation and NO reduction reactions, both relevant to three-way catalysis. In particular, the use of copper and chromium as co-dopants is shown to have a synergistic effect, with significant improvement in reducibility and oxygen storage capacity compared with single-dopant and undoped ceria nanorod catalysts. Due to this, enhanced low-temperature activity for both CO oxidation and NO reduction is seen, beyond that of typical three-way catalyst designs which rely on platinum group metal catalysts.

Graphene oxide has been utilised as a sacrificial template to synthesise two-dimensional ceria nanoflakes. Due to this morphology, ceria nanoflakes demonstrate improved resistance to sintering at high temperatures compared to untemplated ceria particles and retain higher levels of reducibility and oxygen storage capacity. This correlates with a higher catalytic performance for CO oxidation. Additionally, using ceria nanoflakes as a catalyst support for metal particles results in a more stable catalyst than using untemplated ceria. This is demonstrated for copper/ceria catalysts with CO oxidation and nickel/ceria catalysts for dry reforming of methane.

Date of Award	4 Sept 2019
Original language	English
Awarding Institution	University of Bath
Supervisor	Salvador Eslava Fernandez (Supervisor), Kevin Robinson (Supervisor) & Laura Torrente-Murciano (Supervisor)